A packet-oriented bus includes data buses that transmit data between devices in the form of packets. PCIe is an example of a packet-oriented bus. PCIe is a serial bus that includes, among other things, a switch fabric to control point-to-point serial connections between devices. PCIe also includes a root complex device to connect a microprocessor and memory to the PCIe switch fabric. In some systems, the microprocessor executes software to determine times at which events occur on the PCIe bus. For example, in response to a processor interrupt, the software determines the time that an event occurred and records that time.